Switch a glyph for a new Instance

Glyphs
1

Hello,
I’m working on a font with two instances.
But I would like to have two different “a” for example:

On the first Instance I will use the glyphs “a” as the main one,
but for the second Instance I would like to assign “a.ss01” as “a”, through Custom Parameters.

If my question is not clear, please let me know.

Thank you.
G

2

There are two options:
https://www.glyphsapp.com/tutorials/alternating-glyph-shapes-with-multiple-axes
https://www.glyphsapp.com/tutorials/alternating-glyph-shapes